Devices are known that may be implanted within a patient's body to monitor one or more physiological conditions and/or to provide therapeutic functions. For example, sensors or transducers may be located deep within the body for monitoring a variety of properties, such as temperature, pressure, strain, fluid flow, chemical properties, electrical properties, magnetic properties, and the like. In addition, devices may be implanted that perform one or more therapeutic functions, such as drug delivery, defibrillation, electrical stimulation, and the like.
Often it is desirable to control or otherwise communicate with such devices once they are implanted within a patient, for example, to obtain data, and/or to activate or deactivate the implanted device. An implant may include wire leads that extend from the implant to an exterior surface of the patient, thereby allowing an external controller or other device to be directly coupled to the implant. Alternatively, the implant may be remotely controlled or communicated with using an external induction device. For example, an external radio frequency (RF) transmitter may be used to communicate with the implant. In addition, RF devices have been suggested that may be implanted within a patient's body to communicate with another implant at another location within the patient's body.
RF energy, however, may only penetrate a few millimeters within a body, because of the body's dielectric nature, and therefore may not be able to communicate effectively with an implant that is located deep within the body. RF devices may also require substantial electrical power, because the devices generally consume electrical energy even when in a dormant state. In addition, although an RF transmitter may be able to induce a current within an implant, the implant's receiving antenna, generally a low impedance coil, may generate a voltage that is too low to provide a reliable switching mechanism.
In a further alternative, magnetic energy may be used to control or otherwise communicate with an implant, since a body generally does not attenuate magnetic fields. The presence of external magnetic fields encountered by the patient during normal activity, however, may expose the patient to the risk of false positives, i.e., accidental activation or deactivation of the implant. Furthermore, external electromagnetic systems may be cumbersome and may not be able to effectively transfer coded information to an implant.
Accordingly, it is believed that apparatus and methods for communicating with implants using acoustic telemetry would be useful.